We are searching for compounds and mechanisms that cause oncogene-selective lethality. Such compounds would eliminate tumor cells harboring specific oncogenic mutations, but have minimal effects on normal cells lacking these mutations. Small molecules with such selective lethality may reveal novel functions of oncogenes and allow for the creation of more selective drugs. In this continuing project, we are defining a novel mechanism for eliminating selectively tumor cells with oncogenic RAS proteins. Using high-throughput screening of 70,000 compounds in isogenic, engineered tumor cell lines, we discovered five novel compounds that are selectively lethal to oncogenic-RAS-expressing cells. With the tools of synthetic chemistry, molecular biology and proteomics, we discovered that voltage dependent anion channels (VDACs) are target proteins for one of these compounds, which we named erastin. In this continuing application, we propose (i) to define the mechanism by which modulating VDAC activity leads to RAS-selective lethality, (ii) to validate VDACs as erastin targets, (iii) to define the downstream consequences of oncogenic RAS signaling that lead to erastin sensitivity and (iv) to test optimized erastin analogs in mouse cancer models. We discovered that erastin acts through the mitochondrial VDAC proteins to cause an oxidative, non- apoptotic death. Erastin thus revealed that oncogenic RAS signaling causes increases VDAC levels and that VDACs are novel gain-of-function targets for cancer therapeutics. Our results support the notion of using small molecules to study oncogene function and suggest that VDAC ligands are potential chemotherapeutic agents for the treatment of cancers with activated RAS signaling. [unreadable] [unreadable] [unreadable] [unreadable]